Redox state of early magmas

Scaillet, Bruno; Gaillard, Fabrice

doi:10.1038/480048a

Cited by 28 publications

(14 citation statements)

References 14 publications

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“…Different variations of this experimentw erep erformed by considering other extraterrestrial conditions that gave rise to several other important molecules relatedt op rebiotic chemistry, such as sugars, [5] polypeptides, [6] and many other small molecules. [7,8] A few years after Miller's experiment, another classic experiment was conducted by Oró, [9,10] in which adeninew as synthesized by heatingamixture of HCN,a nd aqueous ammonia.Although the conditions used to mimic those on the early Earth were different than those used by Miller, [11,12] these experiments remain proof-of-concept that these two classes of fundamental buildingb locks of life-aminoa cids and nucleobases-canb e formedb yc hemical reactions.…”

Section: Introductionmentioning

confidence: 83%

“…A few years after Miller's experiment, another classic experiment was conducted by Oró, in which adenine was synthesized by heating a mixture of HCN, and aqueous ammonia. Although the conditions used to mimic those on the early Earth were different than those used by Miller, these experiments remain proof‐of‐concept that these two classes of fundamental building blocks of life—amino acids and nucleobases—can be formed by chemical reactions.…”

Section: Introductionmentioning

confidence: 89%

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Prebiotic Chemistry of HCN Tetramerization by Automated Reaction Search

Nandi

Bhattacharyya

Anoop

2018

Chemistry A European J

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HCN oligomerization is considered to be one of the important pathways in chemical evolution. Nucleobases, aminoacids, and many other complex organic molecules can evolve through this pathway. We report an explorative study based on an automated reaction search method that avoids the cognitive bias present when searching chemical reaction space. We discuss the chemical space of the HCN dimer in detail, and the important trimers and tetramers are discussed briefly. A component-wise molecular-fingerprint-based methodology is proposed to identify molecular similarity. We present four different thermal routes to cis/trans-2,3-diaminomaleonitrile and 4-amino-1H-imidazole-5-carbonitrile, which are important intermediates in prebiotic chemistry.

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Section: Introductionmentioning

confidence: 83%

Section: Introductionmentioning

confidence: 89%

Prebiotic Chemistry of HCN Tetramerization by Automated Reaction Search

Nandi

Bhattacharyya

Anoop

2018

Chemistry A European J

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“…oxygenpoor), which may lead to conditions that promote high levels of H2 outgassing. One of the main arguments for a reduced early mantle is that Earth (and possibly other terrestrial planets) must have entered a magma ocean stage during accretion, which would have acted as a surficial oxygen sink (e.g., Scaillet and Gaillard, 2011). Afterwards, planetary mantles are thought to become oxidized over time, either gradually or in a stepwise fashion (Wood et al, 2006).…”

Section: Discussionmentioning

confidence: 99%

A Volcanic Hydrogen Habitable Zone

Ramirez

Kaltenegger

2017

ApJL

116

118

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The classical habitable zone is the circular region around a star in which liquid water could exist on the surface of a rocky planet. The outer edge of the traditional N2-CO2-H2O habitable zone (HZ) extends out to nearly ~1.7 AU in our Solar System, beyond which condensation and scattering by CO2 outstrips its greenhouse capacity. Here, we show that volcanic outgassing of atmospheric H2 on a planet near the outer edge can extend the habitable zone out to ~2.4 AU in our solar system. This wider volcanic hydrogen habitable zone (N2-CO2-H2O-H2) can be sustained as long as volcanic H2 output offsets its escape from the top of the atmosphere. We use a singlecolumn radiative-convective climate model to compute the HZ limits of this volcanic hydrogen habitable zone for hydrogen concentrations between 1% and 50%, assuming diffusion-limited atmospheric escape. At a hydrogen concentration of 50%, the effective stellar flux required to support the outer edge decreases by ~35% to 60% for M -A stars. The corresponding orbital distances increase by ~30% to 60%. The inner edge of this HZ only moves out ~0.1 to 4% relative to the classical HZ because H2 warming is reduced in dense H2O atmospheres. The atmospheric scale heights of such volcanic H2 atmospheres near the outer edge of the HZ also increase, facilitating remote detection of atmospheric signatures.

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“…This self-oxidation process ( Fig. 1), may well have contributed to the progressive oxidation of the silicate Earth during accretion, at least during its ultimate stages, and may have also been the trigger of the Great Mantle Oxidation event (Delano, 2001;Scaillet and Gaillard, 2011;Williams et al, 2012), which is a major shift in redox conditions of the Earth's mantle, passing from IW-2 just after the core-mantle separation, to FMQ+0.5/-2 (IW+3/+4.5), as recorded by the oldest mantle rocks (Canil, 1997;Delano, 2001;Canil, 2002;Li and Lee, 2004). Occurrence of oxidized 4.4 Ga old zircons of inferred mantle provenance (Trail et al, 2011;fig.…”

Section: Accepted Manuscriptmentioning

confidence: 98%

“…Identifying variations in mantle redox state both in time and space and capturing the parameters that control redox state inside the Earth is the kernel of a wide and active debate in Earth and planetary sciences (Ballhaus et al, 1991;O'Neill et al, 1993;Ballhaus and Frost, 1994;Canil, 1997;Delano, 2001;Canil, 2002;Frost and McCammon, 2008;Hirschmann, 2009;Kelley and Cottrell, 2009;Scaillet and Gaillard, 2011;Trail et al, 2011;Foley, 2012;Lee et al, 2012;Keller and Schoene, 2012;Bali et al, 2013;Yang et al, 2014). The second issue is about whether the redox state of basalts and associated volcanic gases reflects their mantle source regions (Carmichael and Ghiorso, 1986;Carmichael, 1991;Lee et al, 2005;Mallmann and O'Neill, 2009;Kelley and Cottrell., 2012;Moussallam et al, 2014), and if not, what are the processes likely to change magma redox state upon ascent to the Earth's surface (e.g., Carmichael and Ghiorso, 1986;Carmichael and Ghiorso, 1990;Gaillard et al, 2011;Kelley and Cottrell, 2012;Iacono-Marziano et al, 2012b;Moussallam et al, 2014).…”

Section: Introduction: Oxygen Fugacity and Redox Transfersmentioning

confidence: 98%

The redox geodynamics linking basalts and their mantle sources through space and time

et al. 2015

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International audienceThe Earth's mantle redox state regulates the fate and transfer of metals by magmatism, buffers the igneous inputs of volcanic gases in the atmosphere and controls the depth of mantle melting. It therefore strongly affects ore forming processes, biogeochemical cycles and deep geodynamic processes. This paper reviews the current knowledge on the redox state of the upper mantle and of magmas produced by mantle melting. The geochemical processes likely to control and modify it through space and time are discussed.We analyze the link between the redox state of magma and that of their mantle source and we conclude that melts produced in the mantle may well all equilibrate in a narrow range of oxidation state, where the speciation of sulfur in basalts shifts from sulfide to sulfate, that is, FMQ+1 ± 1 (1 log unit below and above the oxygen fugacity buffered by the assemblage fayalite–magnetite–quartz). Subsequently, degassing and partial crystallization of melts can affect their redox states, producing most of the range of redox states observed on magmas reaching Earth's surface. The asthenosphere sourcing basaltic magmas may therefore be more oxidized than the FMQ−1 value generally assumed.We also discuss redox transfers from the mantle to the atmosphere via volcanic degassing and the backward fluxes via subduction processes of the hydrothermalized oceanic lithosphere. Arc-magmas are oxidized (up to FMQ+4) but it is unclear when this feature is acquired since strongly oxidized primary arc-basalts have yet to be found. The oxidizing event may be the assimilation of slab-derived SO3-rich fluids by primary basalt generated by decompression melting in the mantle-wedge.Overall, subduction must result in a transfer of oxygen from the Earth's surface down to the mantle. This must imply that subduction and its initiation can hardly be the trigger of the great oxidation event at the end of the Archaean. In contrast, the cooling of the Earth's interior through time must have impacted on the redox state of basalts, by decreasing the depth of mantle melting. According to the long-established vertical stratification of the Earth's mantle, ancient primary magmas are therefore likely to have been more reduced (i.e. < FMQ−3) than present-day ones. However, geochemical observations on ancient basalts suggest a constant oxidation state since the early Archaean.We conclude that large uncertainties in the calibration of mineralogical oxygen barometer probably explains why we have difficulties in identifying (i) ancient primary basalts being more reduced than recent ones and (ii) primary basalts from subduction zones being as oxidized as arc-lavas reaching the surface. Finally, the degree of mantle melting is certainly a key issue for the interpretation of the mantle oxidation state. Extremely oxidized melts, enriched in C–H–S volatile species, produced by very low degrees of mantle melting may be indicative of an Earth's mantle more oxidized than usually considered

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Redox state of early magmas

Abstract: International audienceA study of cerium in zircon minerals has allowed an assessment of the redox conditions that prevailed when Earth's earliest magmas formed. The results suggest that the mantle became oxidized sooner than had been though

Cited by 28 publications

References 14 publications

Prebiotic Chemistry of HCN Tetramerization by Automated Reaction Search

Prebiotic Chemistry of HCN Tetramerization by Automated Reaction Search

A Volcanic Hydrogen Habitable Zone

The redox geodynamics linking basalts and their mantle sources through space and time

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